Fluoropolymers such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymers (FEP), perfluoro alkoxylated polyfluoroolefins (PFA), and related fluorocarbon and chlorofluorocarbon polymers are good laminate materials because of their heat resistance, chemical inertness, low permeability, and low coefficient of friction over a wide temperature range. The fluorine atoms act as a protective sheath surrounding the carbon--carbon backbone. It is this fluorine sheath which imparts the chemical inertness found in polymeric fluorocarbons. The porosity and permeability of these polymers can be controlled by varying sintering conditions, that is by heating the polymer above its melting point and allowing it to cool down at varying rates (slower cooling yields higher crystallinity as disclosed in U.S. Pat. No. 5,234,751). Likewise, varying the methods by which the thermoplastic resin is stretched will produce lattices of varying porosity.
Fluoropolymers can be homopolymerized in one of two different procedures, yielding either a granular resin or a dispersion. For example, with respect to the homopolymerization of tetrafluoroethylene (TFE), a granular resin can be precipitated out of the reaction solution if little or no dispersing agent is used and if vigorous agitation is maintained, while a colloidal suspension can be obtained from the reaction solution if sufficient emulsifying agent is employed and if only mild agitation is employed to avoid precipitation of the resin.
While the granular resin can be molded into various forms, the resin dispersion can be used to dispersion coat substrates, or it can be converted into a powder. This powder subsequently can be used to form fibers or films, or it can be combined with a lubricant medium and extruded as a paste, which can be formed, stretched, and/or compressed into various forms such as fibers or films (see, e.g., U.S. Pat. No. 5,234,751).
Other fluorocarbons, such as fluorinated ethylene-propylene copolymer (FEP) or perfluoroalkoxy resin (PFA), can be employed in many of the same applications as PTFE. These other compounds share the chemical inertness, heat resistance, and low coefficient of friction of PTFE, and many of these other fluorocarbons have the added advantage of greater thermoplasticity. These other polymers, therefore, can be more easily processed than PTFE.
Because of their inherent chemical, physical, and electrical characteristics, fluorocarbon-based polymers have been utilized extensively as protective coatings, filtration media, and electrical insulation, as well as in water repellent but breathable fabrics. Metallized composite materials containing such fluorocarbon polymers have been employed as thermal control materials (see, e.g., U.S. Pat. No. 5,227,230), electrically conductive materials (see, e.g., U.S. Pat. No. 5,190,813), fire resistant fabrics, and electromagnetic shielding devices.
Fluorocarbon polymers such as PTFE and FEP are particularly well suited for many filtration applications. These fluorocarbon polymers also are used extensively in the chemical industry as a barrier material because they exhibit low permeability to many fluids. The permeability to liquids and gases of such barrier materials can be reduced by increasing the degree of crystallinity of the polymer, thereby decreasing the interstitial spaces of the polymeric lattice.
The benefits of such fluoropolymer products derive in large part from the hydrophobic characteristics of fluoropolymers. In some applications, however, it is desirable to have a product which exhibits oleophobic, in addition to hydrophobic, characteristics. While polymeric products can be rendered oleophobic by a suitable coating of an oleophobic polymer, the application of such a coating to fluoropolymers is difficult as a result of the repellancy characteristics inherent to fluoropolymers. In addition, such an oleophobic coating can have a tendency to mask the hydrophobic properties of the underlying fluoropolymer.
Previous combinations of hydrophobic and oleophobic fluoropolymers, e.g., in aqueous antiwicking compositions (see, e.g., U.S. Pat. No. 4,868,042) have proven useful, but compositions exhibiting improved fluid repellency are desirable. Moreover, it would be desirable if such liquid compositions had an improved ability to penetrate and thereby coat porous, particularly microporous, substrates to render those substrates both hydrophobic and oleophobic. In addition, hydrophobic and oleophobic compositions which can be formed into porous membranes, nonporous films, fibers, and the like would be particularly useful.
Thus, there remains a need for a fluoropolymer composition and products prepared from or using such a composition which possess significant levels of both hydrophobicity and oleophobicity. The present invention provides such a composition and products utilizing the composition. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.